1. Field of the Invention
The present invention relates to apparatus and methods for electronically correcting the line of sight alignment of an optical system stabilized by a two axis or three-axis gyroscope system, and more particularly, apparatus and methods for calculating and storing data representative of pitch and yaw error signals at time of installation of the gyroscope system in a vehicle and thereafter utilizing such stored data to compensate the pitch and yaw control systems.
2. Description of the Prior Art
A number of military weapons systems include a stable platform for mounting optical devices for sighting of targets. The platform is controlled by a set of roll, pitch and yaw gyros via servomechanisms. A typical system is the Target Acquisition and Designation System (TADS) in which a lens system is focused on a vidicon television camera which drives a television (TV) display. When the system is attached to a fixed or rotary wing aircraft, the pilot can observe the terrain, within the field of view of the optics, on the TV display. The pilot may manually bring a desired target into the center of the display screen and then switch the system to a tracking mode. Thereafter, the stable platform will remain fixed in space with the optics aimed at the target while the aircraft maneuvers.
Each of the three gyros in the stabilization system has a sensitive axis which its associated servo will maintain in a fixed direction in inertial space when the system is in the stabilized mode. The pitch and yaw axes define a plane with an axis perpendicular thereto defined as the stabilization axis. As may now be recognized, the stabilization axis will remain fixed in space as the aircraft moves. If the optical axis of the camera lens system is not exactly aligned with the stabilization axis, the image or picture on the TV screen will not remain centered but will appear to move in an arc as the aircraft experiences roll, pitch and yaw movements. Thus, when a TADS unit is installed, it is necessary to mechanically adjust the platform and television optical system to ensure that the line of sight (LOS) is aligned with the stabilization axis within less than 1 milliradian (mr). Such mechanical adjustment is difficult and time consuming, even for skilled technicians. After a system is in service, it is possible for misalignment to occur from accident or upon replacement of failed mechanical components. Such circumstances may require the aircraft to be returned to a repair facility having the test equipment and trained personnel to readjust the system. Thus, a need has existed for automating the LOS alignment procedure to reduce the labor and time required for manual adjustment, to obtain increased accuracy, and to permit field alignment.